1. Field of the Invention
The present invention relates to a rupturable member that ruptures due to pressure or an impact wave, and more particularly relates to a rupturable member in which reproducibility of the rupturing manner is improved, and that designed rupturing and stable rupturing can be reliably performed.
2. Description of the Related Art
Rupturable members, formed of thin metals, that rupture by generated pressure or an impact wave are used in a large number of apparatus in which, for example, explosives, pressurized fluids and various members are utilized. Examples of devices formed using explosives include a variety of gas generators mounted in automobiles such as gas generators for air bags and gas generators for pretensioners, and in these devices too, rupturable members that rupture as a result of the activation of an igniter which constitutes an activation initiating device or as a result of pressure or an impact wave generated by the combustion of a gas generating agent to generate a gas are used.
In such gas generators for airbags, a gas generating agent for generating a flame or gas due to combustion is used, and these gas generating agents, for the purpose of protection from humidity, are, in some cases, stored in a thin can formed of a metal such as aluminum or stainless steel. In addition, in hybrid gas generators or pressurized gas generators using a pressurized gas or the like, in general, a rupturable plate formed from a metal such as aluminum or stainless steel is attached to the gas discharge hole in order to seal the pressurized gas.
The thin can and rupturable plate described above are ruptured and opened as a result of pressure increase or an impact wave generated inside the can or inside sealed by the rupturable member, the ruptured shape of the can or rupture plate and the generated fragments can be hardly reproductive and is difficult to predict. And, there is a possibility that the fragments produced by the opening and rupturing of the can or rupturable plate will block the gas passage and destabilize performance of the gas generator, or an airbag device or a seat belt pretensioner using the gas generator.
Thereupon, with a view of resolving these problems, the provision of a notch or slit in the above rupturable plate has been considered. JP-A No. 2002-255006 is one example of a patent document pertaining thereto, and in this publication, the provision of a cross-shaped notch in the rupturable plate used for sealing the pressurized gas.
However, if a notch or a fragile portion is provided in the rupturable plate, crack may occur and the rupturable plate may rupture with this as the point of origin, and sometimes, the break thereof may extend to sections in which no notch is provided. That is, if a cross-shaped notch is provided in the center of a rupturable plate in which the perimeter edge is fixed, the rupturing of the rupturable plate may extend to the outer perimeter edge of the rupturable plate beyond the tip ends of the notch, and consequently, the fine fragments may be produced and block the gas passage.
U.S. Pat. No. 5,803,492 shows, in FIGS. 8 and 9, a housing selectively pre-weakened for an air bag inflator.